1. Field of the Invention
The invention is directed to an improved unipolar transverse flux machine.
2. Brief Description of the Prior Art
A known unipolar transverse flux machine is disclosed in European Patent Disclosure EP 0 544 200 A1 and refaced to in that publication as a hybrid synchronous machine with transverse magnetic flux. In this machine, the toothing of each rotor ring has one row of teeth extending along the outer circumference of the rotor ring, remote from the rotor axis, and another set of teeth extending along the inner circumference of the rotor ring, oriented toward the rotor axis, both rows having the same tooth pitch. The rows of teeth on each rotor ring are offset from one another by one tooth pitch. The yoke spacing on the stator corresponds to the tooth pitch of an inner or outer row of teeth, so that an outer tooth of one rotor ring and an inner tooth of the other rotor ring are always located simultaneously under one stator yoke. The two rotor modules, each comprising two rotor rings and one permanent-magnetic member for generating a radial magnetic flux in opposite directions in the rotor rings, are firmly fastened, on the sides remote from one another in the axial direction of the rotor, to a rotor body that is braced on the housing via rotary bearings. Each permanent-magnetic member is formed by a permanent magnet ring fastened between the rotor rings, which is magnetized unipolarly in the direction of the rotor axis. The stator yokes of each stator module that are received by the housing are U-shaped, and with their yoke legs oriented parallel to the rotor axis they fit over the inner and outer rows of teeth of the two rotor rings of the rotor modules. In each stator module, the circular annular coil, disposed concentrically to the rotor axis, passes through the stator yokes at the base of the yoke; that is, it is located in the region between the annular face of the outer rotor ring, pointing away from the rotor body, and the crosspiece of the stator yokes.
Transverse flux machines with permanent magnet excitation are known from the literature, such as Michael Bork, Entwicklung und Optimierung einer fertigungsgerechten Transversalflussmaschine, Diss, 82, RWTH Aachen[Development and Optimization of a Transverse Flux Machine Suitable for Production, Dissertation No. 82, Rheinland-Westfalen Technical University in Aachen], Shaker Verlag, Aachen, 1997, page 8 ff. The circularly wound stator winding is surrounded by U-shaped yokes of soft iron, which are disposed at twice the pole spacing in the direction of rotation. The open ends of these U-shaped yokes are aimed at the air gap between the stator and the rotor and form the poles of the stator. Facing them, tiny permanent magnet plates are disposed such that the two tiny plates that face the poles of a stator yoke have opposite polarity. For short-circuiting the permanent magnets, which upon rotor rotation are sometimes located between the poles of the stator and have no ferromagnetic short circuit, short-circuit elements are disposed in the stator. They prevent the flux of the permanent magnets from scattering via the yoke legs and the annular coil and lessening the effectiveness of the stator flux concatenation from attenuation of the stator flux. Thus the short-circuit elements lead to a marked enhancement of the performance of the machine.
In a unipolar transverse flux machine of the type defined at the outset, it has already been proposed (in German Patent Disclosure DE 100 39 466) that the toothing of the rotor rings be provided solely on the outer circumference of the rotor rings, facing away from the rotor axis, and that the stator yokes in the stator module be disposed such that one yoke leg of the stator yokes faces one rotor ring, while the other yoke leg of the stator yokes faces the other rotor ring, each with radial gap spacing. Between successive stator yokes in the direction of rotation of the rotor, a respective short-circuit element is disposed, which extends axially past both rotor rings and faces each of them with the same radial gap spacing. The permanent-magnetic member for generating a magnetic flux extending radially in opposite directions in the rotor rings is formed by a permanent magnet ring, which is fastened between the two rotor rings and is unipolarly magnetized in the axial direction of the rotor. A unipolar transverse flux machine of this kind has the advantage of simple modular construction, with which any desired number of branches of the machine can be achieved by adding or subtracting identically embodied stator modules and rotor modules, or in other words can be constructed in modular fashion. As the number of modular units, each composed of one stator module and one rotor module, increases, the concentricity of the machine is improved, and an initially indexing-like behavior of the machine changes over to continuous concentricity without ripples in the course of the moment. Since the total moment of the machine is the sum of the proportional moments of the module units, the total moment of the machine can be adapted easily to existing requirements.